1. Technical Field
The present invention relates to a conductive adhesive (conductive die bonding agent) for bonding a semiconductor pellet and tab (die bonding). This invention, as another embodiment, relates to a semiconductor pellet bonded to a tab through the conductive adhesive.
2. Prior Art
Semiconductor devices have a structure, for example, in which a silicon-based semiconductor pellet is bonded by a conductive adhesive, such as a conductive epoxy resin or conductive polyimide resin, to the tab which is the attachment site/support for the semiconductor pellet. The semiconductor pellet is also electrically connected to a metal inner lead frame by metal wires, and this assembly is sealed using a sealing resin such as epoxy resin. A tab and lead frame is described in U.S. Pat. No. 4,721,994, issued Jan. 26, 1988, to Mine et al. Because such a semiconductor device is constituted of various types of materials, cracking may develop in the semiconductor pellet or sealant resin in association with semiconductor pellet warming or heating during sealing with the sealant resin due to increased internal strain which originates in mechanical stresses and differences in the materials' thermal expansion. This causes changes in the performance of the semiconductor device and thus raises the drawback of a decline in its reliability.
As a particular matter, it has recently become necessary to increase both the degree of integration and mounting density of semiconductor pellets, and internal strain is promoted by the accompanying upscaling of the semiconductor pellet. Moreover, in order to increase the processability and thermal conduction of semiconductor devices as well as reduce costs, a trend has developed toward copper alloys (relatively high thermal expansion coefficient) from Ni-Fe alloys (relatively low thermal expansion coefficient) with regard to the material making up the tab and metal inner lead frame. As a consequence, the aforementioned drawback is increasingly being looked upon as a problem.
Thus, when a large-scale silicon-based semiconductor pellet is fixed on a copper tab using a prior conductive adhesive such as a conductive epoxy resin adhesive or conductive polyimide resin adhesive, stresses develop due to the difference in thermal expansivity between the copper tab and semiconductor pellet, and the curvature of the semiconductor pellet becomes large. Its properties are altered and in extreme cases cracking develops in the semiconductor pellet, and the decline in the reliability of the semiconductor device can be even greater than before.
In order to solve this problem, a semiconductor device has already been proposed in which the semiconductor pellet and tab are bonded by a conductive adhesive in the form of a conductive silicone rubber (refer to Japanese Patent Application Laid Open [Kokai or Unexamined] Number 58-86732 [86,732/83]), published May 24, 1983. This attempts to use a conductive, elastic silicone rubber to relieve the internal strain originating in the different thermal expansivities of the tab and semiconductor pellet.